The present invention relates to means for compensating for distortion, and more particularly to an optical device compensator for correcting distortions in an intensity modulated optical device.
Where wide bandwidth video signals are transmitted over a fiber optic link, intensity modulated (IM) systems are often used rather than square wave frequency modulated (FM) systems. While properly designed FM systems are essentially immune to amplitude nonlinearities of the optical transmitter and receiver devices, IM systems are directly affected by such nonlinearities. In addition to the simple nonlinear characteristics, optical devices also exhibit signal dependent nonlinearities. For example LED transmitters often have an optical efficiency which is a function of the average drive power, integrated over a time constant on the order of several hundred microseconds. As the average drive power increases, the efficiency, and therefore the optical power output, decreases. This produces dynamic gain variations as a function of the average picture level (APL) in video signals.
What is desired is an optical device compensator which reduces the dynamic gain variations caused by the variation of device output power as a function by the average drive power.